Cerebral Hypoxia-Ischemia Stimulates Cytokine Gene Expression in Perinatal Rats

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Abstract
Background and Purpose We tested the hypothesis that cerebral hypoxia-ischemia selectively stimulates interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) gene expression in brain regions susceptible to irreversible injury in perinatal rats. Methods To elicit focal hypoxic-ischemic brain injury, 7-day-old perinatal (P7) rats were subjected to right carotid artery ligation followed by 3 hours of 8% O2 exposure and were killed 0 to 48 hours after hypoxia. Regional tissue IL-1β and TNF-α mRNA content were measured by reverse transcription followed by polymerase chain reaction amplification (RT-PCR) in samples prepared from cortex and hippocampus of the lesioned and contralateral hemispheres. cDNAs were amplified with primers specific for IL-1β, TNF-α, and the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which served as an internal control. The RT-PCR products were subjected to Southern blot analysis and hybridized with 32P-labeled gene-specific probes. Radioactivity was measured in excised bands, and results were normalized on the basis of levels of GAPDH expression. Results In unlesioned P7 brain, IL-1β mRNA was barely detectable. In lesioned forebrain, there was a marked, transient stimulation of IL-1β mRNA expression, peaking at 4 hours after hypoxia. Hybridization signal was increased 16- to 30-fold over values from contralateral hemisphere samples in three independent assays (P<.05 comparing values in left and right cortex and in left and right hippocampus with the Kruskal-Wallis ranking test); by 24 hours after hypoxia, levels returned to normal. Similar transient increases in TNF-α mRNA expression were detected. In a closely related model of perinatal brain injury elicited by focal intracerebral N-methyl-d-aspartate injection, there was a corresponding acute stimulation of IL-1β and TNF-α mRNA expression at 4 hours after injection. Conclusions These results suggest that IL-1β and TNF-α may play important roles in the response of the developing brain to acute hypoxic-ischemic injury.